1. Field of the Invention
The invention relates generally to methods and apparatus for liquid treatment of wafer-shaped articles, such as semiconductor wafers, wherein one or more process liquids are dispensed onto a surface of the wafer-shaped article.
2. Description of Related Art
Semiconductor wafers are subjected to various surface treatment processes such as etching, cleaning, polishing and material deposition. To accommodate such processes, a single wafer may be supported in relation to one or more treatment fluid nozzles by a chuck associated with a rotatable carrier, as is described for example in U.S. Pat. Nos. 4,903,717 and 5,513,668.
Alternatively, a chuck in the form of a ring rotor adapted to support a wafer may be located within a closed process chamber and driven without physical contact through an active magnetic bearing, as is described for example in International Publication No. WO 2007/101764 and U.S. Pat. No. 6,485,531.
Ordinarily, treatment fluids, especially etching liquids, are dispensed from above onto the upper surface of a rotating wafer which faces away from the chuck. In some instances, as described for example in International Publication No. WO 2009/027194, gas is directed to the opposite back surface, which faces the chuck, to provide a gas cushion between the wafer and the chuck which secures the wafer using the Bernoulli-Effect and/or limits treatment liquid dispensed on the front surface of the wafer from flowing around the wafer's edge to the back surface of the wafer. As is further described in International Publication No. WO 2009/027194, a rinsing liquid may be directed to the back surface of the wafer to remove residues of treatment liquid that may have reached the peripheral region of the back surface of the wafer.
With increasing miniaturization of devices and features fabricated on semiconductor wafers, processing those wafers in an uncontrolled open environment becomes more problematic. For example, when wafers undergo wet processing in stations that are open to the surrounding air, the oxygen content of the air causes unwanted corrosion of copper on the front side of the wafer.
During processing of a single wafer in an open environment the oxygen from the air can diffuse through the liquid layer on the wafer to the wafer surface, leading to copper oxidation and therefore copper loss. This effect is enhanced where the liquid layer is very thin, e.g. at the wafer edge.
Furthermore, mechanical and fluid forces acting across the surface of a wafer during processing in an uncontrolled open environment can lead to pattern collapse, distortion or other damage to various devices and features fabricated on the surface of the wafer.
Pattern collapse can occur, for example, when the surface tension of a liquid moving radially outwardly across the surface of a rotating wafer applies a damaging or destructive force to the submicroscopic structures formed on the wafer surface. The problem of pattern collapse becomes more serious as the diameter of semiconductor wafers increases and as the aspect ratio of the submicroscopic structures increases.
The application and removal of treatment liquids in an uncontrolled open environment also leads to the creation of watermarks on the surface of the wafer.